8 folders cost $8.80. Which equation would help determine the cost of 13 folders?
Explanation: There are several equations that could help determine the cost, each with a slightly different approach. If we let $x$ represent the cost of 13 folders, we have the following proportion: $\dfrac{x}{13}$ We have to pay $8.80 for 8 folders, and that can be written as a proportion: $\dfrac{\$8.80}{8}$ Since the price per folder stays the same, these two proportions are equivalent. $\dfrac{x}{13} = \dfrac{\$8.80}{8}$